Mortars are good against deep pools of Creeps. (but not worth the money if everything is shallow)

Move your City in later parts of a level, so energy has only a short way to your new buildings and weapons.

New buildings are only build when they are connected to finished buildings. They do only order energy to build when they are connected, so a „string“ of new buildings will need much more time than a „cluster“.

Weapons do have some ammo (red line on top of box), so you can fly them somewhere without connections to the grid, but remember to fly them back.

Your weapons and your city do have a health bar, your other buildings do not.

Cross canyons with relays.

You have some time at your hands? Build reactors and storage.

Move your weapons in 2 lines. The first stays still and shoots, the second flies over them to land in front of them, securing the new line.

Drones are to take out huge deep amounts of Creeps, for other things they are a waste of energy.

Mortars can be used as a „poor mans drone“

You need to tell your drones where to attack!

Fly a blaster into the Creeps to make room for a relay. Land the next one when your first one is out of ammo and fly the first one back to reload, continue till relay is ready. This is a fast way to cover wide areas.

One Blaster near a creeper source is normally enough to stop production of new Creeps.